Binder mixture for friction elements comprising phenolic resin and precipitated silicate

ABSTRACT

BINDER RESIN COMPOSITIONS FOR THE PREPARATION OF FRICTION ELEMENTS E.G. BRAKE AND CLUTCH LININGS HAVING GOOD HOT WEAR PROPERTIES COMPRISE FROM 5 TO 95 PARTS BY WEIGHT OF A PHENOLIC RESIN AND FROM 95 TO 5 PARTS BY WEIGHT OF A PRECIPITATED ALKALI METAL SILCATE. THE RESINS MAY BE COMPOUNDED WITH CONVENTIONAL ADDITIVES, E.G. ASBESTOS AND BARYTES AND MOULDED UNDER HEAT AND PRESSURE TO FORM FRICTION ELEMENTS.

AU 112 EX US. Cl. 260-38 8 Claims ABSTRACT OF THE DISCLOSURE Binder resin compositions for the preparation of friction elements e.g. brake and clutch linings having good hot wear properties comprise from 5 to 95 parts by weight of aahanolis-ieoin and from 95 to 5 parts by weight ofa The resins may be compounded with conventional additives, e.g. asbestos and barytes and moulded under heat and pressure to form friction elements.

The present invention is concerned with improved binder resin compositions for the preparation of friction elements, and friction elements prepared therefrom.

Friction elements such as clutch plates and brake linings can be made by bonding a friction material with a resin. Asbestos is commonly used as a friction material, either as a woven fabric or in fibre form. The friction materials are usually bonded with a thermosetting phenolic resin. When such friction elements are subjected to severe brake or clutch operating conditions, the high temperatures produced tend to break down the element with resulting wear and/or loss in frictional properties.

According to the present invention, a binder resin composition suitable for use in the preparation of friction elements having improved hot wear properties, as herein defined, comprises from 5 to 95 parts by dry weight of a phenolic resin and from 95 to 5 parts by dry weight of an alkali metal silicate and an activating precipitant for the alkali metal silicate, as herein defined.

By a friction element having improved hot wear properties is meant throughout this specification a friction element which exhibits a lower weight loss under load at high operating temperatures than a similar friction element compounded from the same phenolic binder resin in the absence of the alkali metal silicate and the precipitant.

Any phenolic resin of the type employed in the manufacture of friction elements can be used according to the present invention. An example of such a resin is one prepared by the reaction of a monohydric or dihydric phenol and an aldehyde under either acid (novolak) or alkaline (resole) conditions. A preferred phenolic resin is one prepared from phenol per se (C H OH) and formaldehyde. However, phenol/ aldehyde resins obtained from cresol, xylenol or other alkyl or aralkyl substituted phenols, resorcinol or cashew nut-shell liquid as all or part of the phenol and furfuraldehyde as all or part of the aldehyde can be employed. The phenolic resin may be modified by known methods with natural or synthetic rubbers or fatty oils or fatty acids and is mixed with curing agents such as for example hexamine and paraform as necessary.

The preferred alkali metal silicate is sodium silicate.

The relative proportions of the phenolic resin and the alkali metal silicate in the binder resin compositions can vary widely to give the desired balance between hot and cold wear properties and frictional properties of the fric- 3,655,609 Patented Apr. 11, 1972 ice tion elements obtained from the binder resin compositions. Particularly useful binder resin compositions are obtained using to 35 parts by dry weight of phenolic resin to 35 to 65 parts by dry weight of alkali metal silicate.

Chemicals that precipitate an alkali metal silicate from solution in a finely divided form are well known. Such chemicals are discussed in A Comprehensive Treatise on Inorganic and Theoretical Chemistry vol. VI by J. W. Mellor (Longmans, Green and Company, London, 1957) at page 291 et seq. By an activating precipitant is meant throughout this specification a chemical that precipitates an alkali metal silicate from solution and satisfies the following test. When present in a phenolic binder resin composition containing an alkali metal silicate it causes friction elements made therefrom to have greater hot wear resistance than similar friction elements compounded from the same phenolic resin in the absence of the alkali metal silicate and the precipitant, the relative.

quantities of the components in the test being:

Phenolic resin-l5 parts by dry weight Alkali metal silicate-l1 parts by dry weight Precipitant4 parts by weight Asbestos-37 parts by weight Barytes33 parts by weight,

and the alkali metal silicate and the precipitant being replaced by 8 parts of asbestos and 7 parts of barytes in the comparative friction element.

Suitable activating precipitants are ammonium chloride, ammonium dihydrogen phosphate, ammonium ortho-phosphate, aluminium sulphate, aluminium oxide, hydrated alumina, boric acid, calcium hydroxide, ferric chloride, hydrochloric acid, sodium bicarbonate, zinc chloride and Hydracrete portland cement. A mixture of equal parts by weight of ammonium chloride and calcium hydroxide is also a suitable activating precipitant.

When using sodium silicate it has been found that ammonium chloride is a particularly effective activating precipitant.

It is preferred to employ an amount of activating precipitant sufficient to cause substantially complete precipitation of the alkali metal silicate from an aqueous solution thereof. It is usually unnecessary to employ a weight of activating precipitant greater than the weight of alkali metal silicate although in many cases any excess precipitant acts as filler in the final friction element without any deleterious effect on the properties thereof.

Suitable friction materials for use in composite friction elements prepared from the binder resin compositions of the present invention are the materials well known in the art, such as asbestos. The compositions may be further modified by the incorporation of known fillers such as for example barytes, metal filings, rubber, organic friction particles and graphite. However, it has been found that certain known fillers e.g. magnesium oxide, interfere with the action of certain activating precipitants, e.g. calcium hydroxide and, therefore, the choice of fillers'will depend to some extent on the precipitant used, in order that friction elements having the desired properties are obtained.

The binder resin compositions of the present invention can be prepared by dry or wet mixing of the necessary components. Conveniently this blending can be carried out at the same time and in the same blender as the mixing of the friction materials in the fabrication of the friction elements.

The friction elements can be made by the known processes for bonding friction materials with resins. For example, the resin can be dry mixed with asbestos and the mix moulded under pressure with heat, or a solution of air the resin can be used to impregnate asbestos by the wet The results are shown in Table 1 and comparison of mix dough process, the solvent being dried otf prior to the hot wear performance of compositions 2, 4 and 6, moulding. Suitably a pressure of at least 1 ton/square containing the alkali metal silicate/activating precipitant inch and a temperature of at least 150 C. should be system of the present invention with compositions l, 3 used in the moulding process. and 5 without an alkali metal silicate, and composition 7 The invention is further illustrated with reference to (Example 2) Without an activating precipitant readily the following examples. shows the improvement in hot wear obtained by using the binder resin compositions of the present invention.

TABLE 1 Disc pad composition Dynamometer test results Parts oi Loss in Friction level Ammoweight, grams before fade at- Sodium nium 5R Composition silichlo- Silasbes- Cold Hot 30 60 Number Resin Number Type of resin Resin l eate ride ica tos Barytes wear wear m.p.h. m.p.h.

Phenol resole 37 33 7.010 9. 622 0.202 0. 184 -do 37 33 1.063 3.008 0.30 0.25 Phenol novolak with 45 40 1. 200 12. 884 0. 305 0. 26

hexamine. 0-...--............-do..--............ 37 33 0.886 3.680 0.236 0.22 Cellobond J 960/644" Elastomer modified 45 40 1. 450 13.110 0. 29 0. 24

nov ak with hexamine. 6 .-do ..do 11 4 37 33 0.750 7. 591 0.25 0. 2o

1 Parts given are parts by dry weight of components. In these compositions the total parts of ingredients add to 100. The organic resin content of the system is maintained at 15 parts throughout, the inorganic content to 85 part (the ratio of asbestos to barytes also being kept constant).

1 Cellobond 1s a reglstered trademark of 13.1. Chemicals (U.K.) Limited.

EXAMPLE 1 EXAMPLE 2 Six compositions, 3 as controls and 3 according to the A further series of compositions were prepared by the present invention were prepared from various phenolic method of Example 1, to show the use of various other resins and fabricated into disc pads. activating precipitants. The base phenolic resin used was \An aqueous sodium silicate solution was used which the hexamine cured phenolic novolak Cellobond I 615 had a specific gravity of 1.50, but quantities are expressed used in compositions 3 and 4 of Example 1. The compoas parts by dry weight of the ingredients. sitions were fabricated into disc brake pads and tested by The procedure for the preparation of the moulded disc the same procedure described in Example 1. The results pads was as follows. Wet mixes were prepared by blending are shown in Table 2, from which it may be seen that all the ingredients in a Z-blade mixer, sufiicient water or inthe disc pad compositions 8-18 containing sodium silicate dustrial methylated spirit being added to give good wetting and an activating precipitant show an improvement in hot and mixing. The wet mixes were dried at 75 C., the drywear over a composition 7 in which no precipitant was ing time being dependent on the time required to give present, and composition 3 of \Example 1 in which the optimum flow of the component under moulding condistraight resin was used. tions. Comparison of the test results on composition number The dry compositions were all moulded at a tempera- 3 of Example series 1 and on composition number 7 of ture of 160 C. and a pressure of 1 ton/sq. in. for 10 Example series 2 shows that the presence of the alkali minutes with breathing for 15 seconds 1 /2 minutes after metal silicate in the composition reduces the hot wear the application of full P Post Stoving 0f the resistance of the formed friction element. However, the moulded pads was carried out for 16 hours at 150 C. presence of an activating precipitant causes a k d i The pads were tested on an inertia dynamometer with crease in the hot wear resistance of the formed friction a proprietary disc brake assembly. The inertia of the elements.

TABLE 2 Dynamom- Disc pad composition eter test, hot wear Parts Parts of (loss in Composition Resin of sodium Preeipitating agent (4 parts Asbesweight Number number Type of resin resin silicate by weight) tos Barytes in grams) 7 Cellobond Phenol novolak 15 11 N n 37 33 17.80

I615. with hexamine.

15 11 Ammonium dihydrogen phosphate. 37 33 9. 57 15 11 Ammonium orthophosphate 37 33 9. 45 15 11 Aluminium oxide 37 33 4. 60 15 11 Hydrated alumina. 37 33 5. 33 15 11 Aluminium sulphate. 37 33 10. 35 15 11 Boric acid 37 33 11. 62 15 11 Calcium hydroxid 37 33 9. 26 5 11 Ferric chloride. 37 33 4. 16 15 11 Concentrate hydroc 37 33 9. 5O 15 11 Hydracrete" portland cemen 37 33 1.3 15 11 Zinc chloride 37 33 5. 1

N o'rE.Composistious 7-18 were wet mixed using sodium silicate solution (S.G. 1.50). All proportions are in parts by dry weight.

machine was set to simulate the energy produced by a EXAMPLE 3 medium weight family saloon. Cold Wear testing was carried out over stops at a temperature of 80 to A further four compositions were prepared by a dry C., whilst the Hot Wear was measured over 15 stops with mixing technique wherein Cellobond 1615 phenolic resin a temperature range as measured by a thermocouple em- 15 parts by dry weight), sodlurn silicate (11 parts by bedded in the centre of the disc, of C. to 650 C. 75 dry weight) and activating precipitant (4 parts by dry weight) were blended until an intimate mixture was obtained and then asbestos (37 parts by weight) and barytes (33 parts by weight) were blended in. Disc pads were then fabricated from the compositions by the method ed with (b) a thermoset binder resin composition comprising an intimate mixture of from about 5 to 95 parts by dry weight of a thermosettable phenolic resin which has been thermoset in the presence of from about 95 to described in Example 1. 5 5 parts by dry weight of an alkali metal silicate and an The pads were tested to determine their hot wear propactivating precipitant for the alkali metal silicate which erties, and the results obtained are-shown in Table 3. increases the hot wear resistance of the friction element.

TABLE 2 Dyna-mom- Disc pad composition eter test, hot wear Parts Parts of (lossin Composition Resin of sodium Precipitating agent (4 parts Asbesweight Number number Type of resin resin silicate by weight) tos Barytes in grams) 19 Cellobond Phenol novolak 15 11 Ammonium chloride 37 33 4.36

.1615. with hexamine. A o m d mm urn GT1 9 15 11 {Calcium hydroxide 2 37 33 11 Calcium hydroxide 37 83 5.0 15 11 Sodium hydrogen carbonate 37 33 11. 74

All proportions are in parts by dry weight.

We claim:

1. A binder resin composition for use in the preparation of friction elements having improved hot wear properties, which comprises an intimate mixture of from about 5 to 95 parts by dry weight of a thermosettable phenolic resin and from about 95 to 5 parts by dry weight of an alkali metal silicate and an activating precipitant for the alkali metal silicate which increases the hot wear resistance of friction elements made from the binder resin.

2. A binder resin composition as claimed in claim 1 wherein the alkali metal silicate is sodium silicate.

3. A binder resin composition as claimed in claim 1 wherein the thermosettable phenolic resin is prepared from phenol (C H OH) and formaldehyde.

4. A binder resin composition as claimed in claim 1 wherein the thermosettable phenolic resin is a novolak resin.

5. A binder resin composition as claimed in claim 1 wherein the thermosettable phenolic resin is a resole resin.

6. A composition as claimed in claim 1 wherein the precipitant is selected from the group consisting of ammonium chloride, ammonium dihydrogen phosphate, ammonium orthophosphate, aluminium oxide, hydrated alumina, aluminium sulphate, boric acid, calcium hydroxide, ferric chloride, concentrated hydrochloric acid, zinc chloride and Hydracrete Portland cement.

7. A friction element suitable for use as a brake or clutch lining having improved hot wear properties, which comprises (a) a major amount of a friction material bond- 8. A friction element suitable for use as a brake or clutch lining having improved hot wear properties, which comprises (a) a major amount of asbestos bonded with (b) a thermoset binder resin composition comprising an intimate mixture of from about 5 to parts by dry weight of a thermosettable phenolic resin which has been thermoset in the presence of from about 95 to 5 parts by dry weight of an alkali metal silicate and an activating precipitant selected from the group consisting of ammonium chloride, ammonium dihydrogen phosphate, ammonium orthophosphate, aluminium oxide, hydrated alumina, aluminium sulphate, boric acid, calcium hydroxide, ferric chloride, concentrated hydrochloric acid, zinc chloride and Hydracrete Portland cement.

References Cited UNITED STATES PATENTS 6/1967 Barnett et al 260-38 1/1951 Carlton 26038 X OTHER REFERENCES MORRIS LIEBMAN, Primary Examiner S. M. PERSON, Assistant Examiner US. Cl. X.R.

106-36, 83; 188251 R, 251 A; l92-107 M 

